Free Online Developer Tools
Browse 22 free online developer tools. Every tool runs entirely in your browser: no upload, no signup, no install.
All tools in this category (22)
JSON Formatter
Format, minify and validate JSON with syntax highlighting.
Use nowBase64 Encode/Decode
Encode and decode Base64 for text and files.
Use nowTimestamp Converter
Convert between Unix timestamp and date-time, seconds/ms.
Use nowRegex Tester
Test regular expressions with live highlighting and groups.
Use nowDiff Checker
Compare two texts line by line with colored differences.
Use nowMarkdown Editor
Write Markdown with live preview and HTML export.
Use nowCSV to JSON Converter
Convert between CSV and JSON both ways with headers.
Use nowHTML Entity Converter
Encode and decode HTML entities including < & etc.
Use nowText Encryptor
Encrypt and decrypt text locally with AES-GCM.
Use nowHash Generator
Compute MD5, SHA-1, SHA-256 hashes of text or files.
Use nowURL Encoder & Decoder
Encode and decode URLs or URI components online.
Use nowJWT Decoder
Decode JWT tokens to inspect header, payload and expiry.
Use nowXML Formatter
Format, minify and validate XML with clear error messages.
Use nowURL Slug Generator
Turn any title into a clean, SEO-friendly URL slug.
Use nowNumber Base Converter
Enter an integer in any base from 2 to 36 to see binary, octal, decimal, hex and base-36 results. Big integers stay exact through BigInt, and every row copies in one click.
Use nowCron Expression Generator
Edit cron expressions field by field across minute, hour, day, month and weekday. See plain-English and Chinese descriptions, the next five run times, and live range validation, all in your browser.
Use nowMeta Tag Generator
Fill in the title, description and page URL to build meta snippets live, with a Google search preview.
Use nowSubnet Calculator
Enter an IPv4 address with a prefix or a subnet mask to get network address, broadcast, usable host range and a binary view.
Use nowTOTP Generator
Paste a Base32 secret or an otpauth URI and get live one-time codes. Choose SHA-1, SHA-256 or SHA-512, 6 or 8 digits, and a 30 or 60 second period. Everything runs locally.
Use nowYAML JSON Converter
Convert YAML to JSON and back online, with three directions, indent options and key sorting. Syntax errors report the exact line and column, all locally.
Use nowChmod Calculator
Toggle permission checkboxes and get octal, symbolic and a ready chmod command
Use nowSQL Formatter
Pretty print SQL with a hand built tokenizer, clause breaks and safe comments
Use nowAbout Developer tools
Developer tools here handle small frequent jobs: format, encode, decode, parse, compare. Paste JSON, a Base64 string or a JWT and get the formatted result or diagnosis right away. JSON errors point to line and column, and the regex tester highlights every match with its capture groups.
What you paste often includes API responses, tokens or user data, so the privacy bar is high. Every tool in this category runs in your browser: nothing is uploaded, nothing is logged, and a refresh clears everything. After the page loads, it keeps working offline.
How to choose the right Developer
- Match tool to data shape
Structured data goes to the JSON/XML formatters, encoding questions to the Base64 and URL tools, tokens to the JWT decoder. Name the shape first, then open that page.
- Check UTF-8 handling for CJK
Chinese text and emoji break naive encoders. Every encoder here converts through explicit UTF-8 and reports a specific reason when decoding fails.
- Validate first, format second
Validation reports errors without changing your input; formatting rewrites the text and needs valid input. When unsure, validate, then format.
- Keep secrets in local tools
Tokens, keys and user data belong only in tools that run locally. Every tool here has no upload and no logging, and a refresh wipes the data.
Common developer mistakes
- Formatting is not validating
A formatter rewrites text; it does not promise the data is valid. Validate first, then format, or a stray comma gets harder to find after reindenting.
- Blame the font for mojibake
Garbled text usually means a wrong character-set assumption, like decoding GBK bytes as UTF-8. Confirm the source encoding before swapping characters.
- Local tools need no judgement
Local processing protects transport and storage, not content. Consider what pasted data could do before any page renders it.